Modular tulip assembly

ABSTRACT

A modular tulip assembly has a rod receiving tulip and a saddle. The saddle is interlockingly held inside a distal portion of the tulip. The saddle has an external locking groove or recess. The tulip has a locking projection. The locking projection is positioned into the external locking groove or recess and holds the saddle in a pre-loaded unlocked state ready to be pushed onto a head of an implanted bone screw. Upon receiving the head of the bone screw, the saddle can be moved distally relative to the tulip to a locked state by moving the locking groove or recess distally past the locking projection to where the proximal end of the saddle is past abutting the locking projection.

ROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/284,929 filed Oct. 4, 2016 titled A MODULAR TULIP ASSEMBLY, which isincorporated by reference herein.

TECHNICAL FIELD

The present invention relates to an improved modular head tulipassembly.

BACKGROUND OF THE INVENTION

Bone anchor screws come in a variety of shapes and sizes. One of themore common styles has a polyaxial head that allows for the screw toenter the bone structure at an ideal or preferred inclination. Toachieve this polyaxial inclination, the head has a shape configured toallow a complimentary implant device being held by the screw to rotateabout its lower external surface. This lower surface can be one of anumber of shapes like conical or spherical or hemispherical. Thisability is often used in rod receiving implant devices having a modularhead assembly.

The modular head pedicle screw assembly generally includes a tulip. Atulip is a body structure having two opposing sides spaced by a slottedopening to receive a spinal rod. The tulip often employs internalthreads to receive a rod locking set screw to anchor or fix the rod inthe tulip. The lower portion of the tulip has an opening to receive thepedicle screw in a base seat. Often, the tulip can have a saddle thatalso supports the rod along an underside of the rod. The saddle havingan upper recessed curvature into which the rod sits and a lower cup likeopening to receive the top of the pedicle screw head. When the saddleand rod and set screw are tightened, the screw angle is fixed againstthe tulip seat.

Often, it is preferred that the pedicle screw is first placed securelyin the bone structure leaving the head protruding above the bonesurface. In this surgical procedure the tulip assembly must be adaptedto fit down onto the projecting screw head. To accomplish this, thesurgeon must push the tulip onto and over the screw head without a clearpath of vision. Accordingly, the placement must be accomplished withoutany way of knowing if the tulip or other device is properly secured.Thereafter, the device is tightened to complete the assembly and theonly way to insure the assembly is secure requires an upward pulling ofthe tightened assembly. This is not a good test because the assembly maybe loosened or the screw to bone interface weakened.

It is, therefore, an objective of the present invention to provide a wayfor a surgeon to place a tulip assembly onto a pedicle screw alreadythreaded into bone in such a way the surgeon can make a proper andsecure connection easily.

It is a further objective that the device has properly fitted the tulipassembly onto the pedicle screw head by the very nature of the design.It is another objective that the device provides a self-locking featurethat when tightened by assembly, the surgeon can lock the assemblyengagement insuring he has made a proper assembly. These and otherobjectives are achieved by the invention as described hereinafter.

SUMMARY OF THE INVENTION

A modular tulip assembly has a rod receiving tulip and a saddle. Thesaddle is interlockingly held inside a distal portion of the tulip. Thesaddle has an external locking groove or recess. The tulip has a lockingprojection. The locking projection is positioned into the externallocking groove or recess and holds the saddle in a pre-loaded unlockedstate ready to be pushed onto a head of an implanted bone screw. Uponreceiving the head of the bone screw, the saddle can be moved distallyrelative to the tulip to a locked state by moving the locking groove orrecess distally past the locking projection to where the proximal end ofthe saddle is past abutting the locking projection.

The tulip has a pair of opposing internally threaded walls defining aslotted opening for receiving a rod, an open bore with an open distalend for passing the polyaxial head of the bone screw, and the lockingprojection is axially spaced below the internal threads of the opposingwalls and above the open distal end.

The saddle has an axis defined by a center opening. The saddle has aproximal end with a concavity for holding a rod and a distal portionwith a plurality of arcuate fingers spaced by slots. The plurality ofarcuate fingers are curved to form at least a hemispherical shapedconcavity for receiving and holding the head of the bone screw. Thefingers extend to a distal end. The saddle has the exterior lockinggroove or recess positioned between the proximal end and above thearcuate fingers. The saddle is sized to pass through the open distal endof the tulip and move axially inside the tulip below the internalthreads. The tulip has an enlarged internal chamber to accommodate thearcuate fingers and sized to allow the fingers to flex outwardly overand past a maximum diameter of the screw head on attachment.

In one embodiment, the saddle center opening at the proximal end hasinternal threads to engage threads of an end of a tool configured toaxially move the saddle relative to the tulip. The saddle ispre-positioned in an unlocked bone screw receiving state when thelocking groove or recess is moved onto the locking projection and afterbeing attached onto an implanted bone screw polyaxial hemisphericalhead, the saddle is configured to be moved relative to the tulip byrotation of the tool to the locked state by moving the locking groove orrecess distally off the locking projection and having the proximal endof the saddle moved distally past and abutting the locking projectioncausing the arcuate fingers at the distal end to flex and be compressedat the open distal end of the tulip. The locked saddle can berepositioned to the unlocked state by attaching the threaded end of thetool to the saddle and rotating the tool as it abuts a proximal end ofthe tulip causing the saddle locking groove or recess to engage thelocking projection and move onto the locking projection allowing thearcuate fingers to release the screw head and the tulip assembly to beremoved from the bone screw.

In a preferred embodiment, a modular tulip assembly is configured toreceive and lock onto an implanted bone screw having a threaded shankand a hemispherical polyaxial head. The tulip subassembly has a tulipand a saddle. The tulip has a pair of opposing internally threaded wallsdefining a slotted opening for receiving a rod, an open bore with anopen distal end for passing the polyaxial head of the bone screw, and alocking projection being axially spaced below the internal threads ofthe opposing wall and above the open distal end. The saddle has an axisdefined by a center opening. The saddle has a proximal end with aconcavity for holding the rod and a distal portion with a plurality ofarcuate fingers spaced by slots. The plurality of fingers are curved toform at least a hemispherical shaped concavity for receiving and holdingthe head of the bone screw. The fingers extend to a distal end, thesaddle has an exterior locking groove or recess positioned between theproximal end and above the arcuate fingers. The saddle is sized to passthrough the open distal end and move axially inside the tulip below theinternal threads. When assembled to the tulip, the saddle ispre-positioned in an unlocked bone screw receiving state when thelocking groove or recess is moved onto the locking projection.Thereafter, the saddle in the unlocked state can be attached onto animplanted bone screw polyaxial hemispherical head. The saddle isconfigured to be moved to a second locked state by moving the lockinggroove or recess distally off the locking projection and having theproximal end of the saddle moved distally past and abutting the lockingprojection causing the arcuate fingers at the distal end of the tulip toflex and be compressed at the open distal end of the tulip.

In this preferred embodiment, the tulip has an enlarged internal chamberto accommodate the arcuate fingers and sized to allow the fingers toflex outwardly over and past a maximum diameter of the screw head onattachment. The saddle center opening at the proximal end has internalthreads to engage threads of an end of a tool configured to axially movethe saddle relative to the tulip. The modular tulip assembly has thesaddle pre-positioned in an unlocked bone screw receiving state when thelocking groove or recess is moved onto the locking projection and afterbeing attached onto an implanted bone screw polyaxial hemisphericalhead, the saddle is configured to be moved relative to the tulip byrotation of the tool to the locked state by moving the locking groove orrecess distally off the locking projection and having the proximal endof the saddle moved distally past and abutting the locking projectioncausing the arcuate fingers at the distal end to flex and be compressedat the distal end of the tulip. The modular tulip assembly allows thelocked saddle to be repositioned to the unlocked state by attaching thethreaded end of the tool to the saddle and rotating the tool as it abutsa proximal end of the tulip causing the saddle locking groove or recessto reengage the locking projection and move onto the locking projectionallowing the arcuate fingers to release the screw head allowing thetulip assembly to be removed from the bone screw.

A method of assembling a modular tulip has the step of providing a tulipwith a distal and a proximal projection; and positioning a saddle with aconcave locking surface inside the tulip over and past the distalprojection and onto the proximal projection inside the tulip in apre-loaded unlocked state to receive a head of a bone screw. The methodfurther has the step of pushing the tulip with the pre-loaded unlockedsaddle onto an implanted bone screw previously threaded into bone andmoving the saddle to a locked state by moving the locking groove orrecess distally off the locking projection and the proximal end distallyabuts the locking projection. The step of moving the saddle to a lockedposition further includes engaging internal threads of the saddle with athreaded end of a tool, rotating the tool to move the saddle from thepre-loaded unlocked state to the locked state after attaching theimplanted screw. The method further has the step of unlocking the lockedtulip assembly by moving the saddle by moving the saddle from the lockedstate to the pre-loaded unlocked state. The step of unlocking isaccomplished by engaging threads of the saddle with the threaded end ofthe tool and rotationally pulling the saddle proximally relative to thetulip.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described by way of example and with reference tothe accompanying drawings in which:

FIG. 1 is a perspective view of the tulip assembly positioned above anexemplary bone screw.

FIG. 2 is an explode perspective view of the tulip and saddle of thepresent invention above an exemplary bone screw.

FIG. 3 is a perspective view of the tulip assembly shown attached to theexemplary bone screw.

FIG. 4 is a cross-sectional view of the tulip assembly in a pre-loadedunlocked state with the saddle shown attached onto the head of anexemplary bone screw.

FIG. 5 is a cross-sectional view showing the tulip assembly wherein aninternal saddle has been moved to the locked position or state.

FIG. 6 is a plan view of a tool end with a threaded end for attaching tointernal threads of the saddle.

FIG. 7 is a cross-sectional view taken from FIG. 6 showing the tool endthreaded into the saddle with the saddle having been moved relative tothe tulip into the locked state.

FIG. 8 is a perspective view of the tool end above the tulip assemblyand bone screw illustrating removal of the tool after locking oralternatively showing how the tool can be used to unlock the saddle toallow the tulip assembly to be removed from an implanted bone screw.

FIG. 9 shows the tulip assembly attached to the tool for eitherattachment to the exemplary bone screw or alternatively after removalfrom the bone screw.

FIG. 10 shows in cross-section the tulip assembly and unlocked saddleattached to the tool for attachment to or alternatively as occurs onremoval from said bone screw.

FIG. 11 is a cross-sectional view illustrating the tulip assembly withthe saddle in a preloaded unlocked state over an exemplary bone screw.

FIG. 12 is a cross-sectional view showing the tulip assembly wherein theinternal saddle has been moved to the locked position or state and anexemplary fixation rod is being held in the proximal end of the saddlesecurely fixed by the exemplary set screw threadingly engaged in theinternal threads of the two opposing walls of the tulip.

FIG. 13 is a perspective view of the tulip of the present invention.

FIG. 14 is a cross-sectional plan view of the tulip taken from FIG. 13.

FIG. 15 is a perspective view of the saddle of the present invention.

FIG. 16 is a plan view of the saddle taken from FIG. 15.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, a perspective view of the modular tulipassembly 10 of the present invention is shown. As shown, the modulartulip assembly 10 has a rod receiving tulip 20, and internal of the rodreceiving tulip 20 is shown a saddle 40, the saddle 40 is interlockinglyheld inside a distal portion of the tulip 20. Below the tulip assembly10, is shown an exemplary bone screw 2. The bone screw 2 has a threadedshank 4 for engaging bone and a rounded spherical or hemispherical head6 at the proximal end of the shank 4. This head 6 is configured toprovide polyaxial movement of the bone screw 2 relative to the tulipassembly 10 on assembly. This polyaxial movement is maintained as longas the tulip assembly 10 is not locked into position and fixed.

The modular tulip assembly 10 is basically a two part device with thetulip 20 and the preloaded saddle 40 for use with a bone screw 2. Thebone screw 2 can be preloaded into the assembly 10 to make a threecomponent device or system if desired. An important feature of thepresent invention is a binary locking aspect where a single lockingprojection 25 in combination with a recess or groove 42 holds the saddle40 in a preloaded state inside the modular tulip 20 and when the modulartulip assembly 10 is moved onto the head 6 of a bone screw 2 the saddle40 can be moved into a locked state and, if desired, can be unlocked ina reversible fashion making the modular tulip assembly 10 mostconvenient to use. These features are fully described in detail asfollows.

With reference to FIG. 2, the modular tulip assembly 10 is shown in anexploded view with the saddle 40 shown below and between the tulip 20and the bone screw 2.

In FIG. 3, the tulip assembly 10 is shown attached to the exemplary bonescrew 2 in a perspective view. The tulip 20 is fully separatelyillustrated in FIGS. 13 and 14.

With reference to FIG. 4, a cross-sectional view of the tulip assembly10 is shown wherein the saddle 40 is positioned over the polyaxialhemispherical head 6 of the exemplary bone screw 2. As shown incross-section, the tulip 20 is shown with opposing walls 22, 23 withinternal threads 24 defining a rod receiving slot or channel 33. Belowthe internal threads 24 is illustrated the saddle 40. The saddle has alocking groove or recess 42 affixed to a locking projection 25 in thetulip 20 of the tulip assembly 10. As further shown, and with referenceto FIGS. 15 and 16, the saddle 40 has a proximal end 44 with a rodreceiving concavity 45 that is aligned with the channel 33 of the tulip20. At the proximal end 44 of the saddle 40 there is a central opening41 that is threaded with threads 43, as illustrated. The locking grooveor recess 42 is shown near the proximal end 44 of the saddle 40. Belowthe locking groove or recess 42 is shown a plurality of axiallyextending flexible fingers 52 that are spaced apart by slots or slits54. At a distal end 51, these arcuate curved flexible fingers 52 arebowed slightly inwardly. At the proximal end of the slot 54 is anenlarged circular hole 55 to provide stress relief and also increase theflexibility of the fingers 52. This is important in that the fingers 52must flex or bow outwardly in order to expand as they slide over thehemispherical head 6 of the exemplary bone screw 2. As shown in FIG. 4,the plurality of arcuate fingers 52 extend downward past the maximumdiameter (d max) of the polyaxial hemispherical bone screw head 6. Thefingers 52 extension creates at least a hemispherical concavity 53 thatextends beyond the maximum diameter d max and as such, the curvature ofthe fingers 52 bends outwardly at the proximal end and bows inwardlytowards the distal end 51, however, when attached to the bone screw 2,all of the fingers 52 are shown deflected outwardly. As shown in FIG. 4and also in FIG. 14, in cross-section, the tulip 20 has a large internalchamber 30 above the distal end 31. This chamber 30 is configured toallow the fingers 52 of the saddle 40 to bow outwardly on assembly. Oncethe fingers 52 have bowed or flexed outwardly to pass the maximumdiameter d max of the bone screw head 6, they will conform or flex backinwardly compressing and sliding against the surface 8 of thehemispherical bone screw head 6. Preferably, the concavity 53 formed bythe plurality of arcuate fingers 52 is sized to complimentarily fit thehead 6 of the bone screw 2 to which it is to be attached.

With reference to the proximal end 44 of the saddle 40, as shown, theproximal end 44 is shown above where the grove or recess 42 ispositioned over a projection 25 in the tulip 20. The outer or exteriorsurface of the proximal end 44 has a small rounded edge or chamfer 48 tofacilitate sliding over the projection 25. When the saddle 40 isoriented in this position, it is in a preloaded and unlocked positionwherein the arcuate extended fingers 52 are allowed to move inwardly andoutwardly relative to an axis of the tulip 20. with reference to FIG. 5,the saddle 40 is shown moved in a locking position wherein the proximalend 44 of the saddle 40 is moved past the locking projection 25 of thetulip 20 and the groove or recess 42 is moved from the lockingprojection 25 and the proximal end 44 of the saddle 40 is move pastabutting the locking projection 25. In this state, the saddle 40 isprevented from any proximal movement relative to the tulip 20 and thearcuate fingers 52 have been pressed into the distal opening 32 of thetulip 20 between the head 6 of the polyaxial screw 2 and the distal end31 of the tulip 20. This causes the arcuate fingers 52 to be flexedinwardly, tightly grasping against the polyaxial head 6 of the bonescrew 2. This assembly can be accomplished when the bone screw 2 isimplanted in bone. In such a case, the modular tulip assembly 10 withthe saddle 40 in the unlocked position can be positioned over the head 6of the bone screw 2, pushed onto the bone screw 2 and thereafter thesaddle 40 moved into the locking position.

With reference to FIGS. 6-10, the tulip assembly 10 is shown attached tothe bone screw 2 with the assistance of a tool 100. The tip 102 of thetool 100, illustrated in FIG. 6, has a threaded end 103, alsoillustrated in FIG. 7 in a cross-sectional view, that is engaged withthe internal threads 43 of the saddle 40. The end 102 of this tool 100is configured to threadingly engage the saddle 40 and in so doingenables the tool 100 to push against the saddle 40, the outer shoulder106 of the tool 100 is adapted and precisely dimensioned to abut aproximal end 27 of the tulip 20 along the opposing walls 22, 23. Whenthis occurs and the internal shaft 101 of the tool 100 is rotated, itwill push the saddle 40 directly axially distally moving the saddle 40from the preloaded unlocked position to the locked position asillustrated in FIG. 7. FIG. 8 shows the tool 100 separated from thetulip assembly 10 as the tool 100 is being removed after the assembly isaccomplished or FIG. 8 can be viewed alternatively as a removal tool 100assisted illustration wherein the tulip assembly 10 when attached andlocked onto an implanted bone screw 2 can be physically removed bythreading the end 103 of the tool 100 into the internal threads 43 ofthe saddle 40 and rotating in such a fashion that is pulls the saddle 40in the proximal direction relative to the tulip 20. When this occurs,the saddle 40 will move from the locked position as the fingers 52 willbe released from the distal end 51 and moved upward into the chamber 30within the tulip 20 as the recess or groove 42 is positioned onto thelocking projection 25, when this occurs, the tool 100 can be used topull the tulip 20 with unlocked saddle 40 away from the implanted bonescrew 2, as illustrated in FIG. 9. It is understood while the bone screwis shown not embedded in bone just for simplification, it is to beappreciated that this procedure can be accomplished while the bone screw2 is implanted in a vertebral body. The cross-sectional view of FIG. 10illustrates how the fingers 52 are allowed to flex when the bone screw 2has been removed and a saddle 40 is prepositioned in the unlocked state.

FIG. 11 shows the tool 100 being removed from the tulip assembly 10.

With reference to FIG. 12, once the assembly is made, it is possible toplace a spinal fixation rod 60 into the concavity at the proximal end 44of the saddle 40. Once the rod 60 is in position, a threaded set screw80 can be driven down into the internal threads 24 of the opposing walls22, 23 of the tulip 20. The set screw 80 will then lock the rod 60 intoposition. When this occurs, the entire assembly is locked into a lockedposition.

While the embodiment shown shows a single projection 25 is used for thelocked position, and a movement of the saddle 40 from an unlockedinitial state with the recess or groove 42 on the projection 25 to alocked position when in use, it is understood that a resistance or forcerequired to move the saddle 40 into the preloaded unlocked position forassembly can be adjusted depending on the amount of interference that isprovided between the projection 25 and the groove or recess 42 and theexterior surface of the proximal end 44 of the saddle 40. It is believedto have sufficient locking strength, it is preferable that the exemplarytool 100 be used so that the forces required to overcome the initialunlocked state where the recess 42 is positioned over the projection 25are such that a tool 100 is preferred. The tool 100 designed provides aforce between the tulip 20 and the saddle 40, but provides not liftingor pulling forces against the bone screw 2 which can be embedded inbone. This is important in that one does not want to loosen a bone screw2 that has been attached into a vertebral body, but rather would likethe forces for locking the saddle 40 in positon relative to the tulip 20be absorbed between the tool 100, the tulip 20 and the saddle 40 withoutany particular axially loads pulling or loosening the bone screw 2.

These and other objectives are achieved by the application of thepresent invention as described above.

To load the saddle 40 in the tulip 20, a tool is required. A load of 50to 250 pounds force is believed to be an acceptable range to move thesaddle 40 in the preloaded unlocked position with the groove 42 movedonto the projection 25, preferably this load averages 100 pounds. Theload to move to the locked position has the same range of 50 to 250pounds, preferably 100 pounds. As these loads are relatively high, thetool is needed. Interestingly, the saddle 40, when unlocked and ready toreceive a pedicle screw head 6, has the plurality of fingers 52configured to easily deflect allowing a surgeon to place the modulartulip assembly 10 onto the head 6 of an implanted bone screw 2 with verylittle force, 2.0 to 20.015, typically 5 pounds or less. This lowpositioning force allows the surgeon to feel the fingers 52 slide overthe screw head 6 past the maximum diameter while the force drops and thefingers 52 slide and move back to an undeflected or less deflectedstate. The fingers 52, once over the screw head, hold the modular tulipassembly in place until the surgeon uses the tool to move the saddle tothe locked position. Thereafter, a rod 60 and set screw 80 can beaffixed to complete the fixation. The pedicle screw 2 of the presentinvention has a major thread diameter of 4.0 mm to 10.5 mm and a lengthof 25 mm to 110 mm. While the locking features of the modular tulipassembly are shown with a tulip 20 and saddle 40 configured to receive apedicle screw 2, it is understood the locking connector or otherassemblies and is not limited to a single rod receiving tulip body.

Variations in the present invention are possible in light of thedescription of it provided herein. While certain representativeembodiments and details have been shown for the purpose of illustratingthe subject invention, it will be apparent to those skilled in this artthat various changes and modifications can be made therein withoutdeparting from the scope of the subject invention. It is, therefore, tobe understood that changes can be made in the particular embodimentsdescribed, which will be within the full intended scope of the inventionas defined by the following appended claims.

What is claimed is:
 1. A method of assembling a tulip assemblycomprising the steps of: providing a tulip with a locking projection;positioning a saddle with a concave locking surface onto the lockingprojection in an unlocked state to receive a head of a bone screw;placing the tulip with saddle onto the head of the bone screw threadedinto bone; and moving the saddle to a locked state by moving the concavelocking surface past the locking projection by engaging internal threadsof the saddle with a threaded end of a tool and rotating the tool toaxially move the saddle from the unlocked state to the locked state onthe head of the bone screw.
 2. The method of assembling a tulip assemblyof claim 1 further comprising the step of: moving the saddle from thelocked state to the unlocked state by engaging internal threads of thesaddle with the threaded end of the tool and rotating the tool toaxially move the saddle proximally relative to the tulip.
 3. The methodof assembling a tulip assembly of claim 2, wherein the tool provides aforce between the tulip and the saddle, without pulling or loosening thebone screw.
 4. The method of assembling a tulip assembly of claim 2,wherein the tool abuts a proximal end of the tulip.
 5. The method ofassembling a tulip assembly of claim 2, wherein an outer shoulder of thetool abuts a proximal end of the tulip.
 6. The method of assembling atulip assembly of claim 2, wherein the tool provides a force between thetulip and the saddle, without providing lifting or pulling forcesagainst the bone screw threaded into bone.
 7. The method of assembling atulip assembly of claim 1 further comprising the step of: moving thesaddle from the locked state to the unlocked state by rotating the tool.8. A method of assembling a tulip assembly comprising the steps of:providing a tulip with a locking projection; positioning a saddle insidethe tulip, wherein the saddle has a locking groove or recess; affixingthe locking groove or recess to the locking projection to position thesaddle in an unlocked state to receive a head of a bone screw; placingthe tulip with saddle onto the head of the bone screw threaded intobone; and moving the saddle to a locked state on the head of the bonescrew by moving the locking groove or recess past the locking projectionby engaging internal threads of the saddle with a threaded end of a tooland rotating the tool to axially move the saddle from the unlocked stateto the locked state on the head of the bone screw.
 9. A method ofassembling a tulip assembly of claim 8 further comprising the step of:moving the saddle from the locked state to the unlocked state byrotating the tool.
 10. A method of assembling a tulip assembly of claim9, wherein the tool abuts a proximal end of the tulip.
 11. A method ofassembling a tulip assembly of claim 9, wherein an outer shoulder of thetool abuts a proximal end of the tulip.
 12. A method of assembling atulip assembly of claim 9, wherein the tool provides a force between thetulip and the saddle, without providing lifting or pulling forcesagainst the bone screw threaded into bone.
 13. The method of assemblinga tulip assembly of claim 9, wherein the tool provides a force betweenthe tulip and the saddle, without pulling or loosening the bone screw.14. A method of assembling a tulip assembly comprising the steps of:providing a tulip with a locking projection; positioning a saddle insidethe tulip, wherein the saddle has a locking groove or recess; affixingthe locking groove or recess to the locking projection to position thesaddle in an unlocked state to receive a head of a bone screw; placingthe tulip with saddle onto the head of the bone screw threaded intobone; engaging internal threads of the saddle with a threaded end of atool; and moving the saddle to a locked state on the head of the bonescrew by moving the locking groove or recess past the locking projectionby rotating the tool.
 15. A method of assembling a tulip assembly ofclaim 14 further comprising the step of: moving the saddle from thelocked state to the unlocked state by rotating the tool.
 16. A method ofassembling a tulip assembly of claim 15, wherein the tool abuts aproximal end of the tulip.
 17. A method of assembling a tulip assemblyof claim 15, wherein an outer shoulder of the tool abuts a proximal endof the tulip.
 18. A method of assembling a tulip assembly of claim 15,wherein the tool provides a force between the tulip and the saddle,without providing lifting or pulling forces against the bone screwthreaded into bone.
 19. The method of assembling a tulip assembly ofclaim 15, wherein the tool provides a force between the tulip and thesaddle, without pulling or loosening the bone screw.